This invention relates to molecular memory systems and methods.
Many different molecular electronic logic and memory devices have been proposed.
For example, in one molecular memory device structure, a molecular layer (e.g., a Langmuir-Blodgett film) is sandwiched between a pair of electrically conducting layers (e.g., a pair of metal layers, a metal layer and a doped semiconductor layer, or a pair of doped semiconductor layers). The molecular layer serves as a thin insulating film that may be used in a metal-insulator-metal (MIM) structure, which may be configured as a tunnel junction device or a switching device, or a metal-insulator-semiconductor (MIS) structure, which may be configured as a logic and memory device.
U.S. Pat. No. 6,128,214 describes another molecular memory device structure that is configured as a molecular electrode crossbar memory (MWCM) system formed from a two-dimensional array of nanometer-scale devices. Each MWCM device is formed at the crossing point (or junction) of a pair of crossed electrodes where at least one molecular connector species operates as a bi-stable molecular switch between the pair of crossed electrodes. The resulting device structure may be configured as a resistor, a diode or an asymmetric non-linear resistor. The state of each MWCM device may be altered by applying a relatively high state-changing voltage and may be sensed with a non-state-changing (or non-destructive) voltage.
U.S. Pat. No. 5,812,516 describes a molecular memory system in which a scanning tunneling microscope probe electrode (or an atomic force microscope probe electrode) is scanned directly above a molecular recording layer and is used to emit electrical signals for writing information to and reading information from localized areas of the molecular recording medium. In operation, the distance between the probe electrode and the recording medium is maintained constant (e.g., on the order of 1 nm) based upon a detected displacement of the probe electrode caused by an inter-atomic force acting between the probe electrode and the recording medium. In this way, damage that might be caused by contact between the probe electrode and the recording medium may be avoided.
Still other molecular memory systems and devices have been proposed.
The invention features a novel molecular memory system that includes a protective layer that is disposed over a molecular recording layer to enable a scanning probe to write information to and read information from a molecular memory element by direct electrical contact without substantial risk of damage to either the scanning probe or the molecular recording medium. In this way, the invention avoids the high emission currents, which may damage the probe electrode or the recording media, or both; and avoids other difficulties often associated molecular memory systems with non-contacting probe electrodes.
In one aspect, the invention features a molecular memory system that includes a first electrode structure, a second electrode structure, and a recording medium having a molecular recording layer disposed between the first electrode structure and the second electrode structure. The second electrode structure has a substantially planar protective surface exposed for contact with a probe tip and comprises an array of spaced-apart electrodes separated by electrically insulating material.
Embodiments in accordance with this aspect of the invention may include one or more of the following features.
The molecular recording layer preferably comprises a switchable molecular species (e.g., a rotaxane molecular species). The molecular recording layer preferably has a memory property selectively holding first and second memory states with different current-voltage characteristics and preferably exhibits transition between the first and second memory states upon application of a state-changing voltage across the recording layer. The first electrode structure preferably comprises metal layer disposed over a substrate. The second electrode structure preferably comprises an array of spaced-apart metal electrodes separated by a metal oxide (e.g., aluminum electrodes separated by aluminum oxide).
In some embodiments, the molecular memory system includes a probe tip that is configured to contact the exposed substantially planar protective surface of the second electrode structure. The probe tip preferably comprises a carbon nanotube. A scanning assembly may include an array of probe tips, each of which is configured to contact the exposed substantially planar protective surface of the second electrode structure. An actuator may be coupled to the array of probe tips and may be configured to adjust the position of the probe tips to maintain contact between each probe tip and the exposed substantially planar surface of the second electrode structure. The scanning assembly preferably is configured to scan the probe tip array across the exposed substantially planar protective surface of the second electrode structure. A read/write controller preferably is configured to control the application of voltage signals through the scanning assembly probe tips and between the first electrode structure and the electrodes of the second electrode structure. The read/write controller preferably is configured to control application of a sensing voltage for determining a local memory state of the molecular recording layer and to control the application of a state-changing voltage for changing a local memory state of the molecular recording layer.
In some embodiments, a lubricant is disposed over the exposed substantially planar protective surface of the second electrode structure.
In another aspect, the invention features a method of making the above-described molecular memory system.
In another aspect of the invention, a probe array is contacted against the exposed substantially planar protective surface of the second electrode structure of the above-described molecular memory system, and the contacting probe tip array is scanned across the exposed substantially planar protective surface of the second electrode structure.
Other features and advantages of the invention will become apparent from the following description, including the drawings and the claims.